1. Field of the Invention
This invention relates to an ink jet printhead or other microfluidic device having a substantially flat laminated filter and process for fabricating the printhead with such filter.
2. Brief Description of the Prior Art
There are many well known, relatively small fluid handling devices which contain a filter for preventing contaminates entrained in a fluid from entering the device. Generally, the filters are individually assembled in or attached to each separate device during manufacture. A typical example of a small fluid handling device is a thermal ink jet printhead.
A typical thermally actuated drop-on-demand ink jet printing system uses thermal energy pulses to produce vapor bubbles in an ink filled channel that expels drop-lets from the channel orifices of the printing systems printhead. Such printheads have one or more ink filled channels communicating at one end with a relatively small ink supply chamber and having an orifice at the opposite end, also referred to as a nozzle. A thermal energy generator, usually a resistor, is located in the channels near the nozzle and at a predetermined distance upstream therefrom. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. A meniscus is formed at each nozzle under a slight negative pressure to prevent ink from weeping therefrom.
U.S. Pat. No. 4,639,748 to Drake et al. discloses a thermal ink jet printhead composed of two parts aligned and bonded together. One part is a substantially flat substrate which contains on the surface thereof a linear array of heating elements and addressing electrodes. The other part is a flat substrate having a set of concurrently etched recesses in one surface. The set of recesses include a parallel array of elongated recesses for use as capillary filled ink channels having ink droplet emitting nozzles at one end and having interconnection with a common ink supplying manifold recess at the other ends. The manifold recess contains an integral closed wall defining a chamber within the manifold recess and ink fill hole. Small passageways are formed in the top edge of the internal chamber walls to permit passage of ink therefrom into the manifold. Each of the passageways have smaller cross sectional flow areas than the nozzle to filter the ink, while the total cross sectional flow area of the passageways is larger than the total cross sectional flow areas of the nozzle. Many printheads can be made simultaneously by producing a plurality of sets of heating element arrays with their addressing electrodes on a silicon wafer and by placing alignment marks thereon at predetermined locations. A corresponding plurality of sets of channels and associated manifold with internal filters are produced in a second silicon wafer and in one embodiment alignment openings are etched thereon at predetermined locations. The two wafers are aligned via the alignment openings and alignment marks and then bonded together and diced into many separate printheads.
U.S. Pat. No. 4,251,824 to Hara et al. discloses a thermal ink jet printhead having a filter at the ink supply inlet to the printhead. U.S. Pat. No. 4,380,770 to Maruyama discloses an ink jet printhead having an embodiment shown in FIG. 6 that uses a linear array of grooves to filter the ink. The above references disclose the assembly of individual filters for each printhead or the incorporation of integral filters which require more complicated photolithographically patterned printhead parts.
U.S. Pat. No. 4,673,955 to Ameyama et al. discloses an ink reservoir for a drop-on-demand ink jet printer. The reservoir contains a relatively large ink supply chamber and a smaller ink chamber. Ink from the smaller chamber is in communication with the ink jet printhead. The larger ink supply chamber is hermetically sealed and in communication with the smaller chamber through a filter.
U.S. Pat. No. 4,864,329 to Kneezel et al. discloses an ink jet printhead formed from a pair of silicon wafers, one being a channel wafer having elongated ink channels communicating with an ink manifold on one surface and having fluid passageways communicating with ink inlets on the other surface. The surface having the ink inlets is covered with a dry pressure-transferred adhesive layer and then is laminated to a flat filter, such as of woven stainless steel mesh, to exclude any ink contaminants from entering the ink inlets, passageways, manifolds and channels where they can block the ink jet nozzles.